if you ESC has a BEC it will not run because the voltage is to low
it wint hert the ESC but the motor wont run so you have to eather take the ESC off or find a way to by pass it ( maybe you can fit an aligader clip behind the ESC and conet the batterys right to the motor termanals

Couldnt you plug in the regular battery pack and use a receiver to control the ESC to run the motor at a slow speed? Just make sure it nothing gets too hot and set a timer up to remind you to turn it off.